/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* $Id: CommonURIResolver.java 1804124 2017-08-04 14:13:54Z ssteiner $ */

package org.apache.xmlgraphics.util.uri;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

import javax.xml.transform.Source;
import javax.xml.transform.TransformerException;
import javax.xml.transform.URIResolver;

import org.apache.xmlgraphics.util.Service;

A URI Resolver which supports pluggable entities via the Service mechanism. 
 This resolver will try all resolvers registered as an URIResolver class. For proper operation, the registers URIResolvers must return null if they cannot handle the given URI and fail fast. /**
 * A URI Resolver which supports pluggable entities via the {@link Service}
 * mechanism.
 * <p>
 * This resolver will try all resolvers registered as an {@link URIResolver}
 * class. For proper operation, the registers URIResolvers must return null if
 * they cannot handle the given URI and fail fast.
 */
public class CommonURIResolver implements URIResolver {

    private final List uriResolvers = new LinkedList();

    private static final class DefaultInstanceHolder {
        private static final CommonURIResolver INSTANCE = new CommonURIResolver();
    }

    
Creates a new CommonURIResolver. Use this if you need support for
resolvers in the current context.
See Also:
getDefaultURIResolver.getDefaultURIResolver()/**
     * Creates a new CommonURIResolver. Use this if you need support for
     * resolvers in the current context.
     * @see CommonURIResolver#getDefaultURIResolver()
     */
    public CommonURIResolver() {
        Iterator iter = Service.providers(URIResolver.class);
        while (iter.hasNext()) {
            URIResolver resolver = (URIResolver) iter.next();
            register(resolver);
        }
    }

    
Retrieve the default resolver instance.
Returns:
the default resolver instance./**
     * Retrieve the default resolver instance.
     *
     * @return the default resolver instance.
     */
    public static CommonURIResolver getDefaultURIResolver() {
        return DefaultInstanceHolder.INSTANCE;
    }

    
{@inheritDoc} /** {@inheritDoc} */
    public Source resolve(String href, String base) {
        synchronized (uriResolvers) {
            for (Object uriResolver : uriResolvers) {
                final URIResolver currentResolver = (URIResolver) uriResolver;
                try {
                    final Source result = currentResolver.resolve(href, base);
                    if (result != null) {
                        return result;
                    }
                } catch (TransformerException e) {
                    // Ignore.
                }
            }
        }
        return null;
    }

    
Register a given URIResolver while the software is running. 
Params:
uriResolver – 
           the resolver to register./**
     * Register a given {@link URIResolver} while the software is running.
     *
     * @param uriResolver
     *            the resolver to register.
     */
    public void register(URIResolver uriResolver) {
        synchronized (uriResolvers) {
            uriResolvers.add(uriResolver);
        }
    }

    
Unregister a given URIResolver while the software is running. 
Params:
uriResolver – 
           the resolver to unregister./**
     * Unregister a given {@link URIResolver} while the software is running.
     *
     * @param uriResolver
     *            the resolver to unregister.
     */
    public void unregister(URIResolver uriResolver) {
        synchronized (uriResolvers) {
            uriResolvers.remove(uriResolver);
        }
    }

}